Many of the medical care garments and products, protective wear garments, mortuary and veterinary products, and personal care products in use today are partially or wholly constructed of thermoplastic nonwoven web materials. Examples of such products include, but are not limited to, medical and health care products such as surgical drapes, gowns and bandages, protective workwear garments such as coveralls and lab coats, and infant, child and adult personal care absorbent products such as diapers, training pants, swimwear, incontinence garments and pads, sanitary napkins, wipes and the like. For these applications nonwoven materials provide tactile, comfort and aesthetic properties which can approach those of traditional woven or knitted cloth materials. Nonwoven web materials are also widely utilized as filtration media for both liquid and gas or air filtration applications since they can be formed into a filter mesh of fine fibers having a low average pore size suitable for trapping particulate matter while still having a low pressure drop across the mesh.
Nonwoven web materials have a physical structure of individual fibers or filaments which are interlaid in a generally random manner to form a fibrous web material. The fibers may be continuous or discontinuous, and are frequently produced from thermoplastic polymer or copolymer resins from the general classes of polyolefins, polyesters and polyamides, as well as numerous other polymers. Blends of polymers or conjugate multicomponent fibers may also be employed. Nonwoven materials formed by melt extrusion processes such as spunbonding and meltblowing, and formed by dry-laying processes such as carding or air-laying of staple fibers are well known in the art. In addition, nonwoven materials may be used in composite materials in conjunction with other nonwoven layers as in a spunbond/meltblown (SM) and spunbond/meltblown/spunbond (SMS) laminate materials, and may also be used in combination with thermoplastic films.
Nonwoven materials may be topically treated to impart various desired properties, depending on end-use application. For example, some applications such as components for diapers and other incontinence products and feminine hygiene products call for nonwoven materials which are highly wettable and will quickly allow liquids to pass through them. For these applications it is desirable to treat the nonwoven materials with surfactants or other chemicals to impart hydrophilicity. On the other hand, for applications such as surgical drapes and gowns, and other protective garments, liquid barrier properties are highly desirable, and specifically desirable are nonwoven materials which have a high degree of repellency to low surface tension liquids such as alcohols, aldehydes, ketones and hydrophilic liquids, such as those containing surfactants. Repellency to low surface tension liquids may be achieved by treating the nonwoven material with chemicals such as fluorochemical compounds known in the art. Topical treatments are available to impart other properties as well, such as antistatic treatments for example.
Topical treatments are typically applied to fibrous web materials such as nonwoven materials in the form of a treatment chemical carried in a liquid, often aqueous, medium as a solution, suspension or emulsion. Once the treatment has been applied to the nonwoven material it is generally necessary to remove the excess moisture in the nonwoven material sheet by drying. Conventionally, the moisture is removed by blowing heated air on the nonwoven material or by running the nonwoven material over and in contact with heated surfaces such as rollers or cans until it is dry or nearly dry. However, a wetted nonwoven material generally will not dry in all places at the same rate; therefore with conventional drying techniques certain areas of the nonwoven material will become completely dry while other areas still contain moisture, and these areas which dry first will experience continued and excessive heat from the drying process while the entire sheet of material is dried to a satisfactory level of residual moisture. This additional heating of the nonwoven material can deleteriously affect the material and degrade material properties such as by causing heat shrinkage of the material, reducing material tensile strength, causing the material to become embrittled and/or surface glazed and thereby unpleasant to the touch, and decreasing barrier properties in SMS laminate materials.
Consequently, there remains a need for an efficient treatment method that provides treated thermoplastic nonwoven materials without unduly negatively impacting the material and material properties compared with methods heretofore known.